The suit claims the companies "knowingly permitted" the Islamic State group, referred to in the complaint as Isis, to recruit members, raise money and spread "extremist propaganda" through their social media services.

The Gonzalez suit is similar to a case brought against Twitter in January by the widow of a contractor killed in an attack in Jordan. It includes numerous identical passages and screenshots, although the lawyers in the cases are different.

Facebook and Twitter said the Gonzalez lawsuit is without merit, and all three companies cited their policies against extremist material. Twitter said that it has "teams around the world actively investigating reports of rule violations, identifying violating conduct, and working with law enforcement entities when appropriate".

Facebook said that if the company sees "evidence of a threat of imminent harm or a terror attack, we reach out to law enforcement".

Google said it would not comment on pending litigation, but noted that it has "clear policies prohibiting terrorist recruitment and content intending to incite violence and quickly remove videos violating these policies when flagged by our users".

Under US law, internet companies are generally exempt from liability for the material users post on their networks. Section 230 of the 1996 Communications Decency Act provides a legal "safe harbour" for companies like Twitter and Facebook. It says that "no provider or user of an interactive computer service shall be treated as the publisher or speaker of any information provided by another information content provider".